Physical or chemical contamination is very detrimental to miniaturized electronic devices such as LCD, conductive thin film, and integrated circuit. As the size of such a microelectronic device is more compactly reduced, the contamination due to dust is a great factor adversely contributing to the yield rate and defective proportion of production. This augments the necessity of cleaning microelectronic devices.
In order to resolve such problems, there have been proposed various methods of cleaning microelectronic surfaces.
U.S. Pat. No. 5,294,261 discloses a system for cleaning microelectronic surfaces using an Ar or N2 aerosol as a cleaning medium. This system provides a process for cleaning microelectronic surfaces comprising the steps of refrigerating highly pure and highly pressurized argon and nitrogen to a temperature in the range of −160° C. to −200° C. so as to form a cryogenic substance, expanding the cryogenic substance at a low pressure by passing through a nozzle or valve to thereby generate an aerosol consisting of fine solid particles, and making the aerosol impinge upon the microelectronic surfaces. In this case, the argon and nitrogen as cleaning mediums should be cooled down to a very low temperature, which are hardly maintained at solid phase in the atmosphere because of high temperature difference, and therefore the cleaning process must be performed mostly in a vacuum.
Another U.S. Pat. No. 5,486,132 discloses a system for cleaning microelectronic surfaces using a CO2 aerosol as a cleaning medium. In this case, the carbon dioxide as the cleaning medium is refrigerated by a cooling device to a relatively higher temperature in the range of −80° C. to −100° C.
The cooling device used in the above-mentioned systems include a heat exchanger containing liquefied nitrogen as the refrigerant with a temperature of −198° C. or less, through which the cleaning medium is refrigerated. Such cooling device employing the liquefied nitrogen suffers a drawback that the cleaning medium may be over-refrigerated because of difficulties in temperature control. If the cleaning medium is over-refrigerated, it may be solidified before being expanded after passing through the heat exchanger and block the passageway of the conduit and the nozzle. In order to prevent such event increased is the pressure of the cleaning medium, but it increases consumption of the cleaning medium. Moreover, the cooling device requires liquefied nitrogen to be continuously supplied to the heat exchanger, resulting in consumption of a great amount of liquefied nitrogen.